Reflective photomask, method for manufacturing same and program for making mask pattern

ABSTRACT

A reflective photomask includes a substrate and a reflective layer on the substrate. The reflective layer has a top surface opposite to the substrate and a reflectivity distribution on the top surface. The reflective layer includes mask patterns, the mask patterns having sizes depending on the reflectivity distribution. The mask patterns include a first pattern and a second pattern, the first pattern having a first space size smaller than a second space size of the second pattern. The first pattern is provided in a first region of the top surface, and the second pattern is provided in a second region of the top surface, wherein a reflectivity in the first region is lower than a reflectivity in the second region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2015-051706, filed on Mar. 16, 2015; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments are generally related to a reflective photomask, a methodfor manufacturing the same and a program for making a mask pattern.

BACKGROUND

A lithography technique using a EUV light (Extreme Ultra Violet light)in the wavelength range around 13.5 nm is being developed formanufacturing a semiconductor device with a fine structure, such as aMEMS (Micro Electro Mechanical Systems), and the like. A reflectivephotomask used for the lithography in the extremely-short wavelengthregion comprises, for example, a multilayer film mirror, which includesalternately stacked molybdenum (Mo) layer and silicon (Si) layer, and alight-absorbing body. Further, such a reflective photomask is requiredto have a high-level uniformity in a pattern size thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a reflectivephotomask according to an embodiment;

FIGS. 2A to 3B are schematic cross-sectional views showing amanufacturing process of the reflective photomask according to theembodiment;

FIG. 4 is a schematic view showing an exposure apparatus according tothe embodiment;

FIG. 5 is a flow chart showing a method of manufacturing the reflectivephotomask according to the embodiment;

FIGS. 6A to 6C are schematic views showing a property of a photomaskblank according to the embodiment;

FIGS. 7A to 9B are graphs showing characteristics of the exposureapparatus according to the embodiment;

FIG. 10 is a schematic view showing a distribution of an overallreflectivity against exposure light corresponding to positions in thephotomask blank according to the embodiment;

FIGS. 11A and 11B are schematic views showing relationships between apattern size on a wafer and an exposure amount and between a patternsize on a wafer and a mask pattern size; and

FIG. 12 is a schematic view showing a distribution of size adjustmentfactors of a mask pattern corresponding to positions in the photomaskblank according to the embodiment.

DETAILED DESCRIPTION

According to an embodiment, a reflective photomask includes a substrateand a reflective layer on the substrate. The reflective layer has a topsurface opposite to the substrate and a reflectivity distribution on thetop surface. The reflective layer includes mask patterns, the maskpatterns having sizes depending on the reflectivity distribution. Themask patterns include a first pattern and a second pattern, the firstpattern having a first space size smaller than a second space size ofthe second pattern. The first pattern is provided in a first region ofthe top surface, and the second pattern is provided in a second regionof the top surface, wherein a reflectivity in the first region is lowerthan a reflectivity in the second region.

Embodiments will now be described with reference to the drawings. Thesame portions inside the drawings are marked with the same numerals; adetailed description is omitted as appropriate; and the differentportions are described. The drawings are schematic or conceptual; andthe relationships between the thicknesses and widths of portions, theproportions of sizes between portions, etc., are not necessarily thesame as the actual values thereof. The dimensions and/or the proportionsmay be illustrated differently between the drawings, even in the casewhere the same portion is illustrated.

There are cases where the dispositions of the components are describedusing the directions of XYZ axes shown in the drawings. The X-axis, theY-axis, and the Z-axis are orthogonal to each other. Hereinbelow, thedirections of the X-axis, the Y-axis, and the Z-axis are described as anX-direction, a Y-direction, and a Z-direction. Also, there are caseswhere the Z-direction is described as upward and the direction oppositeto the Z-direction is described as downward.

FIG. 1 is a schematic cross-sectional view showing a reflectivephotomask 1 according to an embodiment. The reflective photomask 1includes a substrate 10, a reflective layer 20, and a cap layer 30. Thereflective layer 20 has a multilayer structure. The reflective layer 20is provided on the substrate 10, and the cap layer 30 is provided on thereflective layer 20. The reflective photomask 1 includes a recessedportion 40 that is dug from an upper face of the cap layer 30 into thereflective layer 20. The recessed portion 40 acts as, for example, alight absorbing part or a lower reflection part. The substrate 10 is,for example, a transparent glass substrate.

The reflective layer 20 has a structure in which a first film 22 and asecond film 24 are alternately stacked. The first film 22 differs inrefractive index from the second film 24. That is, the reflective layer20 has a multi-layer structure in which two layers each having adifferent refractive index are alternately stacked. The first film 22is, for example, a molybdenum (Mo) film, for example, and the secondfilm 24 is, for example, a silicon (Si) film. The cap layer 30 is, forexample, a ruthenium (Ru) layer.

The recessed portion 40 has an opening that has a predetermined shape asa mask pattern in a top surface of the reflective layer 20. Although therecessed portion 40 has a structure obtained by digging the reflectivelayer 20 in this example, the embodiment is not limited thereto. Forexample, the reflective photomask 1 may have a structure, in which amaterial serving as a light absorber is selectively disposed on thereflective layer 20 instead of the recessed portion 40.

Furthermore, each recessed portion 40 in FIG. 1 represents a part of apredetermined mask pattern, for example. Hereinafter, a distance betweenthe adjacent recessed portions 40 will be referred to as a space size ofthe mask pattern. Further, each recessed portion 40 may be a crosssection of a sub-pattern included in a predetermined mask pattern, forexample.

Next, referring to FIGS. 2A to 3B, a method for manufacturing thereflective photomask 1 according to the embodiment will be described.FIG. 2A to FIG. 3B are schematic cross-sectional views sequentiallyshowing the manufacturing process of the reflective photomask 1.

FIG. 2A shows a photomask blank 3 prepared. The photomask blank 3includes, for example, the substrate 10, the reflective layer 20, thecap layer 30, and a hard mask 50. The cap layer 30 may be omitted insome instances. The hard mask 50 is provided on the cap layer 30. Thehard mask 50 is, for example, an inorganic film that is capable ofselectively removing from the cap layer 30 and reflective layer 20.

As shown in FIG. 2B, a resist mask 60 is formed on the hard mask 50. Theresist mask 60 has, for example, an opening 60 a. The opening 60 a has apredetermined mask pattern shape in the top surface thereof. The resistmask 60 is, for example, a chemical amplification-type positive resist.The opening 60 a is drawn on the resist film by using an electron beam(EB) exposure apparatus, and then, formed by developing the resist film,for example.

As shown in FIG. 3A, an opening 50 a is formed by selectively removingthe hard mask 50 using the resist mask 60. That is, the mask pattern ofthe resist mask 60 is transferred to the hard mask 50.

As shown in FIG. 3B, the recessed portion 40 is formed by selectivelyremoving the reflective layer 20 using the hard mask 50. In thisexample, the substrate 10 is exposed in the bottom surface of therecessed portion 40 by removing the reflective layer 20 over the wholethickness thereof, but a part of the reflective layer 20 may be leftbelow the bottom of the recessed portion 40. Then, the reflectivephotomask 1 is completed by removing the hard mask 50.

Next, referring to FIG. 4, an exposure apparatus 5 according to theembodiment will be described. FIG. 4 is a schematic view illustratingthe exposure apparatus 5. The exposure apparatus 5 includes a lightsource 71, a mask stage 73, a wafer stage 75, an irradiation part 77,and a projection part 79.

The mask stage 73 holds, for example, the reflective photomask 1. Forexample, a wafer 7 coated with a photoresist is placed on the waferstage 75.

The irradiation part 77 irradiates the reflective photomask 1 with anexposure light L_(ex), which is emitted from the light source 71. Theirradiation part 77 includes mirrors MP₁ to MP₆ to introduce theexposure light L_(ex) to the reflective photomask 1.

The projection part 79 projects the mask pattern of the reflectivephotomask 1 onto the wafer 7. The projection part 79 includes mirrorsMS₁ to MS₆ to focus the exposure light Le_(x) onto the wafer 7.

Next, referring to FIG. 5 to FIG. 12, a method for adjusting a size ofthe mask pattern will be described according to the embodiment. In thefollowing description, the shape of the light absorbing part or thelower reflection part in the top surface of the reflective layer 20 isreferred to as the “mask pattern”, for example. That is, the “maskpattern” is a shape of the opening of the recessed portion 40, forexample. Further, the distance between the adjacent recessed portions40, i.e., the width of the reflective layer 20 between the adjacentrecessed portions 40 is referred to as the “space size”.

For example, when each recessed portion 40 corresponds to a part of themask pattern, the space size may be a distance between the parts of themask pattern. When each recessed portion 40 corresponds to a sub-patternthat is included in the mask pattern, the space size may be a distancebetween the sub-patterns.

FIG. 5 is a flowchart showing the method for adjusting a size of themask pattern according to the embodiment. Hereinafter, steps S101 toS108 for adjusting the mask pattern size shown in FIG. 5 will besequentially described.

Step S101: A distribution of reflectivity in the photomask blank 3 isdetermined. For example, FIG. 6A is a graph illustrating a reflectancespectrum R_(S) of the photomask blank 3 in the EUV wavelength region.The horizontal axis represents the wavelength, and the vertical axisrepresents the reflectivity. The reflectance spectrum R_(S) is oneexample in a region among a plurality of regions which divides a surfaceof the photomask blank 3.

As shown in FIG. 6A, the reflectivity of the photomask blank 3 dependson a wavelength of incident light, and has a peak at approximately 13.5nanometer. Here, the peak wavelength is designated by λ_(P), and acenter wavelength of the reflectance spectrum R_(S) is designated byλ_(C). When the half-value wavelengths are designated by λ₁ and λ₂, atwhich the reflectivity becomes half the peak value, the centerwavelength λ_(C) is a center between λ₁ and λ₂. As shown in FIG. 6A, apeak wavelength λ_(P) does not always coincide with the centerwavelength λ_(C).

FIG. 6B illustrates a distribution of the center wavelengths λ_(C) onthe surface of the photomask blank 3. The horizontal axis and verticalaxis represent the coordinates with a center of the photomask blank 3 asan origin.

FIG. 6C illustrates a distribution of the peak values of thereflectivity on the surface of the photomask blank 3. The horizontalaxis and the vertical axis represent the coordinates with the center ofthe photomask blank 3 as the origin.

As shown in FIGS. 6B and 6C, the peak value and the center wavelengthλ_(C) of the reflectance spectrum R_(S) are distributed in the surfaceof the photomask blank 3. Further, it may be found that the distributionof center wavelengths λ_(C) and the distribution of the peak values ofthe reflectance spectrum R_(S) do not always coincide with each other.

Step S102: An overall reflectivity is calculated at the wafer 7, i.e. anend of a path of the exposure light L_(ex). Here, a ratio of anintensity of the exposure light L_(ex) at the surface of the wafer 7 toan intensity of the exposure light L_(ex) emitted from the light source71 is referred to as the “overall reflectivity” or “overallreflectance”. That is, the “overall reflectivity” is an overallcumulative product of reflectivities through the exposure light path,which includes the reflective mirrors MP₁ to MP₆ in the irradiation part77, the reflective photomask 1, and the reflective mirrors MS₁ to MS₆ inthe projection part 79.

For example, FIG. 7A shows a reflectance spectrum R_(SM) that isobtained by multiplying a reflectance spectrum of the irradiation part77 by a reflectance spectrum of the projection part 79. The horizontalaxis represents the wavelength of the exposure light L_(ex), and thevertical axis represents the normalized reflectivity.

FIG. 7B shows a reflectance spectrum R_(SB1) of the photomask blank 3.The horizontal axis represents the wavelength of exposure light L_(ex),and the vertical axis represents the normalized reflectivity. Forexample, the surface of the photomask blank 3 is divided into theregions each having 1 mm square, and the reflectance spectrum R_(SB1) isdetermined in one of the regions. The horizontal axis represents thewavelength of exposure light L_(ex), and the vertical axis representsthe normalized reflectivity.

FIG. 7C shows an overall reflectance spectrum R_(SW1) obtained bymultiplying the reflectance spectrum R_(SM) by the reflectance spectrumR_(SB1). The horizontal axis represents the wavelength of exposure lightand the vertical axis represents the normalized reflectivity.

FIG. 8A shows another reflectance spectrum R_(SB2) of the photomaskblank 3. The horizontal axis represents the wavelength of exposure lightL_(ex), and the vertical axis represents the normalized reflectivity.The reflectance spectrum R_(SB2) is normalized by the peak value of thereflectance spectrum R_(SB1) shown in FIG. 7B. Further, the reflectancespectrum R_(SB2) is determined in another region different from the oneregion in which the reflectance spectrum R_(SB1) is determined. As shownin FIG. 8A, the reflectance spectrum R_(SB2) shifts to a longerwavelength side than the reflectance spectrum R_(SB1).

FIG. 8B shows another overall reflectance spectrum R_(SW2) obtained bymultiplying the reflectance spectrum R_(SM) by the reflectance spectrumR_(SB2). The horizontal axis represents the wavelength of exposure lightL_(ex), and the vertical axis represents the normalized reflectivity.The overall reflectance spectrum R_(SW2) is normalized by the peak valueof the overall reflectance spectrum R_(SW1) shown in FIG. 7C.

As shown in FIG. 8B, a peak value of the overall reflectance spectrumR_(SW2) decreases as compared with the peak value of the overallreflectance spectrum R_(SW1). That is, the peak value of the overallreflectance spectrum R_(SW) is found to decrease due to a shift of thecenter wavelength λ_(C) of the reflectance spectrum in the photomaskblank 3.

FIG. 9A shows other reflectance spectrum R_(SB3) of the photomask blank3. The horizontal axis represents the wavelength of exposure lightL_(ex), and the vertical axis represents the normalized reflectivity.The reflectance spectrum R_(SB3) is normalized by the peak value of thereflectance spectrum R_(SB1) shown in FIG. 7B. The reflectance spectrumR_(SB3) is determined in other region different from the regions inwhich the reflectance spectrum R_(SB1) and the reflectance spectrumR_(SB2) are determined respectively. As shown in FIG. 9A, thereflectance spectrum R_(SB3) has a peak value of the reflectivitysmaller than the reflectance spectrum R_(SB1).

FIG. 9B shows other overall reflectance spectrum R_(SW3) obtained bymultiplying the reflectance spectrum R_(SM) by the reflectance spectrumR_(SB3). The horizontal axis represents the wavelength of exposure lightL_(ex), and the vertical axis represents the normalized reflectivity.The overall reflectance spectrum R_(SW3) is normalized by the peak valueof the overall reflectance spectrum R_(SW1) shown in FIG. 7C.

As shown in FIG. 9B, a peak value of the overall reflectance spectrumR_(SW3) is smaller than the peak value of the overall reflectancespectrum R_(SW1). That is, the peak value of the overall reflectancespectrum R_(SW) is found to be decreased as the peak value of thereflectance spectrum R_(SB) of the photomask blank 3 becomes lower.

As described above, the peak value of the overall reflectivity maychanges due to a shift of the center wavelength λ_(C) or a fluctuationof the peak value in the reflectance spectrum R_(SB) of the photomaskblank 3. Accordingly, the overall reflectivity on the wafer 7 may becalculated more accurately by determining the reflectance spectrumR_(SB) in each region that divides the surface of the photomask blank,comparing with a case where a distribution of reflectivity in thesurface of the photomask blank 3 is determined at a specific wavelength.

FIG. 10 shows a distribution of overall reflectivity corresponding to acoordinate on the photomask blank 3. The overall reflectivity shown inFIG. 10 is an integrated value obtained by integrating the overallreflectance spectrum R_(SW) over the wavelength in each region of thephotomask blank 3. That is, FIG. 10 shows a distribution of areas of theoverall reflectance spectrum R_(SW) at each coordinate on the photomaskblank 3. A region MP shown in FIG. 10 indicates, for example, a regionin which the recessed portion 40 is formed. The region MP has a size of104 mm×132 mm, for example.

Step S103: Adjusting amounts of the mask pattern size are calculatedusing the overall reflectivity shown in FIG. 10.

FIG. 11A is a graph illustrating a relationship between an exposureamount and the space size in a pattern transferred onto the wafer 7,when the space size in a mask pattern is set constant. The horizontalaxis represents the exposure amount and the vertical axis represents thespace size in the pattern transferred onto the wafer 7. The exposureamount is a product of intensity of the exposure light L_(ex) and anexposure time. For example, an exposure amount E_(X1) in a first regionis larger than an exposure amount E_(X2) in a second region, when anoverall reflectivity corresponding to the first region is larger than anoverall reflectivity corresponding to the second region. Thus, a spacesize S₁ transferred from the first region becomes larger than a spacesize S₂ transferred from the second region.

FIG. 11B is a graph showing a relationship between a space size in amask pattern and a space size in a pattern transferred onto the wafer 7,when the exposure amount is set constant. It can be said that the spacesize in a mask pattern is a design value. That is, the horizontal axisrepresents the design value of the space size, and the vertical axisrepresents the space size in the pattern transferred onto the wafer 7.

For example, the space size S₁ in a pattern transferred onto the wafer 7corresponds to a design value D_(S1), and the space size S₂ in anotherpattern transferred onto the wafer 7 corresponds to a design valueD_(S2). When making the space sizes S₁ and S₂ to be coincident with eachother, a difference ΔD_(S) between the design values D_(S1) and D_(S2)can be used as an adjusting amount. For example, the space size S₁ ismade to be coincident with the space size S₂ by narrowing the space sizeD_(S1) in the first region by the adjusting amount ΔD_(S).Alternatively, the space size D_(S2) in the second region may beenlarged by the adjusting amount ΔD_(S).

FIG. 12 shows a distribution of the adjusting amount in the surface ofthe photomask blank 3. FIG. 12 shows the adjusting amount correspondingto the coordinates with an origin thereof at the center of the photomaskblank 3. A size adjusting coefficient (=[D_(S)−ΔD_(S)]/D_(S)) is shownin this example, wherein a space size D_(S) is a design valuecorresponding to the smallest overall reflectivity (see FIG. 10). It isfound that the size adjusting coefficient decreases as the overallreflectivity increases, comparing the distribution of overallreflectivity in FIG. 10 with the distribution of size adjustingcoefficients in FIG. 12.

Step S104: Data is derived to form a mask pattern in the photomask blank3. The mask pattern is designed and quantified for storing the maskpattern data in a database, for example.

Step S105: The whole mask pattern that is to be formed in the region MPof the photomask blank 3 is divided into a plurality of regions, andeach region includes a part of the whole mask pattern. The whole maskpattern may have a plurality of mask patterns, for example. An MEEF(Mask Error Enhancement Factor) value is calculated for each region. Forexample, the whole mask pattern is divided into a plurality of portionseach having an area of 1 mm square, and the MEEF value is calculated foreach portion. For example, the MEEF value is calculated on the basis ofan average line width or an average space size in each portion of thewhole mask pattern.

The “MEEF value” is a factor obtained by dividing a first deviationamount of a first mask pattern transferred onto a wafer by a seconddeviation amount of a second mask pattern on a photomask, for example,wherein the first deviation amount is a difference in size between afirst mask pattern and a designed mask pattern, and the second deviationamount is a difference in size between the second mask pattern and thedesigned mask pattern. By adjusting the designed size of the maskpattern on the basis of the MEEF value, non-uniformity due to inaccuracyin the manufacturing process of the reflective photomask 1 is suppressedin the transfer pattern on the wafer, for example.

Step S106: The mask pattern data is adjusted. For example, the maskpattern data is adjusted using a size adjusting coefficient at eachcoordinate of the photomask blank 3 shown in FIG. 12. Furthermore, themask pattern data is adjusted using the MEEF value in each region of thephotomask blank 3 corresponding to each portion of the whole maskpattern. The uniformity of the mask pattern transferred onto the wafermay be further improved by adjusting the mask pattern data using theMEEF value.

The MEEF value becomes larger as the space size decreases, for example.Accordingly, in a region having a smaller space size, the mask patterndata is adjusted so that the space size becomes wider. The MEEF value isthe same in the portions that have the same design value of the spacesize. Thus, the adjustment using the overall reflectivity makes thespace size wider in a region where the overall reflectivity is smaller,and narrower in a region where the overall reflectivity is larger. Forexample, the minimum space size corresponding to the resolution limit ofEB exposure apparatus is set to be wider in the region where the overallreflectivity is smaller.

Step S107: A mask pattern is formed using an EB exposure apparatus. Forexample, the mask pattern data adjusted using the overall reflectivityand MEEF value is stored in a database of the EB exposure apparatus, anda resist film formed on the photomask blank 3 is subjected to EBexposure on the basis of the mask pattern data. Then, the resist mask 60is formed on the photomask blank 3 (see FIG. 2B).

Step S108: The light absorbing part (or the low reflection part) isformed in the photomask blank 3. For example, as shown in FIG. 3B, aftertransferring the mask pattern to the hard mask 50, the recessed portion40 serving as the light absorbing part is formed by selectively removingthe reflective layer 20.

For example, light absorbing parts are formed in the photomask blank 3.Each light absorbing part has a sub pattern in the top surface of thereflective layer 20 with a space size depending on the reflectivity of aportion in which each light absorbing part is provided. For example, theminimum space size between first sub patterns that are provided in aportion having a first reflectivity is wider than the minimum space sizebetween second sub patterns that are provided in a portion that has asecond reflectivity, wherein the second reflectivity is higher than thefirst reflectivity. Further, when the first sub pattern and the secondsub pattern each have a similarity shape, the space size between thefirst sub patterns is wider than the space size corresponding thereto inthe second sub patterns. Furthermore, the second reflectivity may belower than the reflectivity in the other portion. The space size betweenthe second sub patterns is wider than the space size between the subpatterns in the other portion.

The above-described steps S102, S103, S105, and S106 are executed by,for example, a computer. A CPU of the computer executes a programincluding: a process of calculating an overall reflectivity based on areflectance spectrum measured in each of a plurality of portions on thesurface of a reflective layer and based on an overall reflectancespectrum of the exposure apparatus; a process of calculating an MEEFvalue of a mask pattern formed in each of the plurality of portions; anda process of adjusting a size of the mask pattern using the overallreflectivity and the MEEF value in each of the plurality of portions. Inaddition, the above-described processes may be executed by, for example,a microprocessor in a control part of the exposure apparatus.

In the method for manufacturing a reflective photomask according to theembodiment, the size of a mask pattern is adjusted on the basis of theoverall reflectivity. Therefore, the uniformity may be improved in awhole mask pattern transferred onto the wafer 7. Furthermore, theuniformity of the transferred pattern may be further improved byadjusting the size of the mask pattern using the MEEF value.

In the method for manufacturing a reflective photomask according to theembodiment, it may become possible to use the photomask blank that isregarded as out of specification in the reflectivity distribution. Thus,the reflective photomask 1 may be manufactured with a lower cost.Furthermore, TAT (Turn Around Time) may also be reduced in themanufacturing process of the photomask blank 3.

In the example described above, although the light absorbing part isprovided with a shape of the mask pattern, the embodiment is not limitedthereto. For example, the reflective layer 20 may have a shape of themask pattern in the upper surface thereof. In such a case, a width ofthe mask pattern is defined instead of the space size, wherein the maskpattern in a portion with higher reflectivity is provided with anarrower width.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A reflective photomask to be provided between a light source and an object to project mask patterns of the reflective photomask on the object using exposure light emitted from a light source, the exposure light propagating through an irradiation part and a projection part via the reflective photomask, the irradiation part being provided between the light source and the reflective photomask to introduce the exposure light to the reflective photomask, and the projection part being provided between the reflective photomask and the object to focus the exposure light onto the object, the reflective photomask comprising: a substrate; and a reflective layer on the substrate, the reflective layer having a top surface opposite to the substrate and including the mask patterns, the mask patterns including a first pattern provided in a first region comprising first plural patterns apart from each other with a first space size and a second pattern provided in a second region comprising second plural patterns apart from each other with a second space size larger than the first space size, the difference of the first space size and the second space size being determined based on an overall reflectivity, the overall reflectivity representing a ratio of an intensity of the exposure light on the object to an intensity of the exposure light at the light source, and the overall reflectivity having a first value at the first region and a second value at the second region, the second value being larger than the first value.
 2. The reflective photomask according to claim 1, wherein the second region has a maximum reflectivity on the top surface; and the second space size is a minimum size among space sizes included in the mask patterns.
 3. The reflective photomask according to claim 1, wherein each of the mask patterns is an opening shape of a recessed portion provided in the reflective layer.
 4. The reflective photomask according to claim 3, wherein the recessed portion extends through the reflective layer from the top surface to the substrate.
 5. The reflective photomask according to claim 1, wherein the reflective layer has a structure in which a first film and a second film are stacked, and the second film is different in a refractive index from the first film.
 6. The reflective photomask according to claim 1, wherein the substrate is a transparent glass substrate.
 7. The reflective photomask according to claim 1, further comprising a cap layer provided on the reflective layer.
 8. A method for manufacturing a reflective photomask to be provided between a light source and an object to project mask patterns of the reflective photomask on the object using exposure light emitted from a light source, the exposure light propagating through an irradiation part and a projection part via the reflective photomask, the irradiation part being provided between the light source and the reflective photomask to introduce the exposure light to the reflective photomask, and the projection part being provided between the reflective photomask and the object to focus the exposure light onto the object, the method comprising: measuring a reflectance spectrum in a wavelength range of the exposure light respectively in a plurality of regions on a surface of a reflective layer of the reflective photomask; determining an overall reflectivity in each of the plurality of regions based on the reflectance spectrum, the overall reflectivity representing a ratio of an intensity of the exposure light on the object to an intensity of the exposure light at the light source, and the overall reflectivity having a first value at the first region and a second value at the second region, the second value being larger than the first value; and adjusting a size of a mask pattern in each of the plurality of regions based on a distribution of the overall reflectivity.
 9. The method according to claim 8, further comprising: determining an MEEF value for the mask pattern in each of the plurality of regions; and adjusting a size of the mask pattern using the MEEF value.
 10. The method according to claim 8, wherein the overall reflectivity is a value obtained by integrating an overall reflectance spectrum over wavelength, the overall reflectance spectrum being obtained by multiplying the reflectance spectrum in each of the plurality of regions by the reflectance spectrum of the irradiation part and the projection part.
 11. The method according to claim 8, wherein the irradiation part and the projection part include a plurality of mirrors; and the reflectance spectrum of the irradiation part and the projection part is an overall reflectance spectrum of the plurality of mirrors.
 12. The method according to claim 8, wherein the exposure light is light in a EUV wavelength region.
 13. The method according to claim 8, wherein the reflective layer has a first region and a second region, the first region having first plural patterns apart from each other with a first space size, and the second region having second plural patterns apart from each other with a second space size larger than the first space size. 